bbm compression levels from a sine wave input

26apr08

The A/D rms values versus mixer input power were
measured using a sine wave input to the baseband mixer chassis. We
wanted to see how large a sine wave we could push through the mixer
chassis before compression set in. This tells us how much of the a/d
dynamic range we will be able to use when a radar signal passes through
the mixer chassis. The setup was:

A 830MHz Sine wave was injected via the if2noise source input
(there was only a sinewave, the noise was disconnected).

This sinewave was mixed to with a 1Ghz lo to 170MHz.

The power was measured using the if2 power meter sitting on beam
5.

This signal was then sent to the bbmixers via the normal path.

The signal was only injected into the low band. Beam 1 had no
signal since that synthesizer was used to generate the birdie.

Before the sine wave was injected, the gain levels in the bbm
were adjusted to give a 30 count rms on input noise. This is the
nominal
setting for using the spectrometer so the compression levels
should reflect what occurs during normal observing.